Spark plugs are used to initiate combustion in internal combustion engines. Spark plugs typically ignite a gas, such as an air/fuel mixture, in a combustion chamber by producing a spark across a spark gap defined between two or more spark plug electrodes. Ignition of the gas by the spark causes a combustion reaction that, in turn, drives a piston within an engine cylinder during a power stroke of the combustion process.
It is desirable to reduce exhaust gas leakage during the combustion process, such as that caused when exhaust gas leaks past the threaded metal shell of the spark plug and out a cylinder head of the engine. In order to reduce or stop such leakage, most spark plugs include a washer-like gasket that becomes compressed between a shoulder of the threaded metal shell and the cylinder head when the spark plug is threadingly installed in the engine. The compressed gasket then creates an air-tight seal between the spark plug and a cylinder head sealing surface.
The effectiveness of the air-tight seal can be impacted by the material or composition of the cylinder head sealing surface against which the spark plug gasket seals. In an effort to reduce vehicle weight, some vehicle manufactures are now utilizing new manufacturing processes, such as lost foam casting, to produce cylinder heads out of certain aluminum and other light weight alloys. Although effective at reducing weight, cylinder heads produced according to such processes are known to have somewhat porous surfaces that are difficult to seal against. This challenge can be further exacerbated when the spark plug gasket is crimped or otherwise deformed during an assembly process so that it no longer has a flat and planar surface to contact and seal against the porous sealing surface of the cylinder head.
It is, therefore, desirable to provide a spark plug gasket that can overcome the porosity and/or other drawbacks of such cylinder head sealing surfaces and create a satisfactorily air-tight seal between the spark plug and the cylinder head.